This invention relates to a needle board for a device for needling a web, comprising a board body made of a light metal alloy, in particular a magnesium-aluminum alloy, and a plastic coating cast onto the board body on the side of the board facing the needle tips.
To obtain a good fixation of the needles on the one hand and on the other hand a good needle guidance in a needle board for a device for needling a web, it is known (AT 392 095 B) to provide the board body with an elastic plastic coating on the side of the board facing the needle tips, before the through holes for the needles are drilled into the needle board. As during this drilling operation in the vicinity of the elastic coating a noticeable elastic displacement of material is obtained, which upon withdrawal of the drills leads to a reduced hole diameter as compared to the subsequent through hole in the board body, the needles, whose needle butts are supported on the board body on the opposite side thereof, can easily be retained by the plastic coating. This holding and guiding function of the plastic coating can, however, only be ensured with a firm connection between the plastic coating and the board body. To prevent a possible detachment of the plastic coating from the board body, the plastic coatings cannot only be bonded, but also be screwed to the board body, which involves, however, an additional effort.
It is therefore the object underlying the invention to design a needle board as described above for a device for needling a web such that a safe connection between the plastic coating and the board body can be ensured without having to accept an additional effort.
This object is solved by the invention in that the board body preferably consisting of a cross-cut extruded section has undercut grooves at its edges on the side of the board covered by the plastic coating, where the plastic coating cast thereon positively fills the undercut grooves.
The formation of the board body as an extruded section offers the simple possibility of providing undercut grooves at the edges, without having to perform an additional machining of the board body, although in special cases it is of course also possible to mill the undercut grooves into the board body by taking an additional effort. However, the board body is advantageously formed of a longitudinal portion of an extruded section, onto which the plastic coating, preferably of polyurethane, is cast. Independent of whether the undercut grooves have been prepared by the corresponding formation of the extruded section or must first be incorporated therein, the plastic material will flow into the undercut grooves and positively fill the same, so that upon curing the plastic coating cast thereon the same is additionally anchored in the undercut grooves of the board body, which involves the required safety with respect to a detachment of the plastic coating from the board body, namely without an additional effort, because the plastic coating must merely be cast onto the board body in a conventional way.
Although different cross-sectional shapes are possible for the undercut grooves of the board body, particularly advantageous constructional conditions are obtained when the grooves at the edges of the board body have a dovetailed cross-section.